The proportion of the elderly in our country (the ratio of people aged 65 or over to total population) was 23.1% in 2010, and is predicted to become as high as 30% in 2025. As the proportion of the elderly in the demographic structure is rapidly increasing, it is urgent to realize a society in which the elderly can live as actively and as healthily as possible without requiring any nursing care, and, even if in need of care, they can live as independently as possible while preventing symptoms from worsening.
In response to the arrival of the aging society, there is an increasing demand for mechanical and electronic devices for physically and mentally supporting the elderly in nursing facilities and households with elderly family members. Also, there are demands not only for physical assistance such as walking aid devices or power assist suits, but also for mental assistance that effectively incorporates robots into work therapies.
One of the important points in the development of mechanical and electronic devices for assistance and care is not to unnecessarily interfere with activities of the elderly but to maintain and facilitate such activities. If a machine carries out activities for an elderly person just because the physical strength of the elderly person has weakened, his/her physical strength will deteriorate further, and the situation worsens (disuse syndrome). A power assist suit is a device that generates an artificial force to reinforce power generated by the muscles of a person. This is a desirable device in keeping an elderly person continuing his/her activities while supplementing the weakening physical strength of the elderly person.
However, the penetration rate of power assist suits is not high at present. The possible reasons for that are as follows.
(1) Wearing it is troublesome.
(2) Only clumsy supports are provided.
(3) It looks bad when worn.
(4) The machine is heavy in weight.
(5) The operating time is short.
For example, attention is recently drawn to a power assist method for giving a drive force to joints based on outputs from myoelectric sensors and results of motion phase estimation (see Non-Patent Document 1, for example). However, as many as nine myoelectric sensors need to be attached to each arm, and it is troublesome to attach those sensors. Also, myoelectric sensors might come off the skin due to deterioration with time or sweat. When the adhesion between a myoelectric sensor and the skin weakens, the output value of the myoelectric sensor becomes unstable. As a result, the power assist suit might run out of control, or an inappropriate force might be applied to the body of the person wearing the power assist suit.
There is also a suggestion for a walking assist device that applies a torque pattern designed in accordance with phases of walking to the body of a person when the person is walking (see Non-Patent Document 2, for example). There are various walking patterns in one user, and the designed torque pattern is often unable to cope with the various patterns. As a result, the user feel uncomfortable while walking, or can walk only in an unnatural manner at a low speed.
Meanwhile, there is a suggestion for a body assist device that does not involve myoelectric sensors (see Non-Patent Document 3, for example). This device senses motions of the joints of the user, and applies supporting forces to the joints. However, if there is hindrance to motions of the joints of the user, it is difficult for this device to reflect intentions of the user at a high sensitivity. For example, the viscous resistance of the gear portions included in the joint units of a conventional power assist suit might cause hindrance to motions of the joints of the user. It is considered that that such impediments need to be eliminated in the future.
Also, forces generated by a power assist suit are often based on an experimental rule or an invalid control law. Ideally, myoelectric sensors can directly reflect a user's intention to move (in reality, however, it is difficult for myoelectric sensors to sense motions in a preferred manner, as described above). On the other hand, it is difficult to read a user's intention from sensed motions of joints. Under such circumstances, it is considered that a valid control law is required so as to provide supporting forces to users without stress and artificiality.
For example, there is a suggestion for a walking assist system that assists walking movements of legs while keeping the user's body balance and supporting the user's body weight (see Patent Document 1, for example). This walking assist system is formed with an inverted-pendulum mobile unit to be held by the user and a walking aid device that assists movements of the legs of the user. A predetermined velocity relationship is to be established between the inverted-pendulum mobile unit and the walking aid device in terms of target moving velocity. The inverted-pendulum mobile unit controls moves based on motions of the base and the target moving velocity when held by the user, and the walking aid device transfers forces to the user based on the motions of the legs of the user and the target moving velocity. However, the walking assist system assists only walking motions, and does not have the versatility to cope with other types of motions of the human body.